1. Field of Invention
The present invention relates to a resonant tag used for the prevention of shoplifting or the like, and more particularly, to a resonant tag that can be made extremely thin for use on very small items while not compromising performance, and which is permanently deactivated when washed or dry cleaned along with a piece of clothing or other washable/dry cleanable article to which it is attached.
2. Description of Related Art
In retail shops, libraries or the like, a surveillance system including a resonant tag that resonates with a radio wave, a transmitting antenna and a receiving antenna has been used for the prevention of shoplifting. The resonant tag is composed of an insulating film, a coil and a plate made of a conductive metal foil formed on one side of the insulating film, and a plate made of a conductive metal foil formed on the other side, which constitute an LC circuit and resonates with a radio wave at a particular frequency. If an article with the resonant tag attached passes through a surveillance area without being checked out, the resonant tag resonates with the radio wave from the transmitting antenna, and the receiving antenna detects the resonance and generates an alarm. A typically used resonant frequency is 5 to 15 MHz, because frequencies within the range can be easily distinguished from various noise frequencies. In electronic article surveillance (EAS), a frequency of 8.2 MHz is most popularly used, and in radio frequency identification (RFID), a frequency of 13.56 MHz is most popularly used.
According to the prior art, even the smallest resonant tag has a significantly large size of 32 mm by 35 mm of rectangular shape and is difficult to attach to small cosmetics items, gems or the like. This is due to the fact that it has been impossible to produce a circuit that has a size meeting the market demand while maintaining the capability of resonating at a frequency of 5 to 15 MHz and maintaining a sufficient gain.
The inventors have previously developed a small tag that has a special configuration in which a coil is formed on each side of an insulating film (see Japanese Patent Laid-Open No. 2001-167366). However, this tag has a disadvantage in that the coil circuits formed on the opposite sides of the insulating film have to be precisely aligned with each other, so that the tag is difficult to manufacture. In addition, there is a problem that, since the metal-foil coils are formed on the both sides of the insulating film, the tag is thick, has a rough touch, is less flexible and is less suitable for handling by a hand labeler.
By way of example only, FIGS. 1-3 depict another prior art resonant tag 10 which includes a coil 11 and a first capacitor plate 12 on one side (FIG. 1) of a substrate 13 and a second capacitor plate 14 on the other side of the substrate 13 (FIG. 2). FIG. 3 is a cross-sectional view of this prior art tag showing a typical substrate thickness, t, of approximately 20 microns, which tends to be the thinnest dielectric that can be formed using conventional dielectric forming methods (e.g., extruding polyethylene between the metal layers). Adhesive layers 15 and 17 secure the metal layers to the substrate 13 respectively.
Prior art resonant tags formed as in FIGS. 1-3 are commonly deactivated, once an article with the resonant tag is purchased, by application of a predetermined voltage to a thinned part of the dielectric to cause dielectric breakdown, thereby making the resonant tag incapable of resonating with a radio wave at a predetermined frequency. A common problem with this type of deactivation means occurs where the tag is incorporated into or attached to an article of clothing. Often, the dielectric heals itself when the clothing is worn or washed. In tags having polyethylene dielectrics, as many as 50% of the tags become reactivated with wearing or laundering. This unintended reactivation has undesirable consequences for the wearer of the clothing, who will activate security tag detection devices when exiting any store with equipment tuned to the tag's resonant frequency. Not only is the false alarm inconvenient and embarrassing for the person wearing the clothing with the reactivated tag, but frequent false alarms can cause a “boy who cried wolf” effect. Store personnel can become lax about enforcement of tag alarms when many of them are falsely triggered by reactivated tags on legitimately purchased goods. Clothing brands bearing re-activatable tags may so irritate consumers that sales are lost. Clearly, a need exists for a security tag for clothing that does not re-activate when washed.
All references cited herein are incorporated herein by reference in their entireties.